1. Field of the Invention
The present invention relates to a method for making metal frameworks for dental protheses:
of the type comprising metallic cops, optionally coated with resin or ceramic materials designed to be anchored in the mouth directly onto the stump of the tooth or teeth to be restored, contiguous or independent,optionally coupled by also metal intermediate members; PA1 using for the embodiment of said cops directly on the master mould, generally of plaster, obtained from the patient maxilla or mandibular cast, i.e. without having to pass through a duplicate in refractory material, first a thin metal sheet forming operation on the stump model of the tooth to be restored and then sintering and/or melting operation of precious, semiprecious and non-precious metal powder, coating said metal sheet, through the effect of a suitable heat supply. PA1 time for making a cop is about 3 hours (cylinder hardening, temperature raising and cooling . . . times). PA1 the material is used in large amounts (overall significant when using precious metals) because cop thickness is at least 0.6 mm with more loss associated to the requirement to forecast casting shafts and several reservations; PA1 the quality of the cop achieved requires a significant adjustment work (porousness because of the gas released during casting, suppression of casting shafts . . . ). PA1 to achieve cops having required mechanical qualities, several layers of base metal are required (because it has to be present in larger amounts than the filler metal) and each time a layer of binding material therefore oxidation problems when melting it; PA1 the layers so obtained does not stand the electrolytic bath (stirrer and temperature); PA1 the interpenetration does not occur in good conditions when melting, therefore homogeneity problems arise in the cops obtained; PA1 it is very hard to separate in good conditions the metal sheet/melt cop; PA1 the classical type binding material does not allow to reduce oxidation; PA1 retraction phenomena of melt metal modify size characteristics of the cops obtained. PA1 directly working on the master model suppressing the step of making a duplicate which is long and expensive; PA1 using sintering and melting techniques of metal alloy powders which allow to obtain half thinner cops (0.3 mm as an average), which means to make economically possible to use semiprecious and precious metals and having a very best aesthetics (suppressing the palatal band); PA1 finding solutions which overcome the problems associated to oxidation, retraction, heterogeneity phenomena of metal sheets: obtained . . . PA1 suppressing adjustment step (namely, scrapping); PA1 working either with non-precious, semiprecious or precious metals.
2. Description of Related Art
Just now the most spread technique in the field of making metal copings for dental protheses is the so-called lost wax process which consists, successively in making the cop (or framework) wax pattern on the master model; to place said pattern in a cylinder (with refractory coating); to locate the assembly in a heating oven to make the wax melt; to cast (in an electronic splint) melt metal (generally a nickel-chromium alloy) which is going to occupy the whole volume left by the wax; to adjust (scraping and sand blasting) the cop achieved.
Above technique shows following drawbacks:
The prior art closest to the technique according to the invention is disclosed in the document FR-A-2660224 (of same applicants) which consists first in forming a 0.02 to 0.03 mm metal sheet on the model involved, then to sprinkle a base metal powder on said sheet so formed previously coated with binding substance, then to coat said particles with a filler metal having a melting point lower than that of the base metal, by Electrodeposition, by metal sublimation or by plasma projection, then to raise the temperature to get binding between filler metal particles and base metal particles, in order to separate the metal sheet from the overlying metal framework so achieved.
The technique involved, which in still at the experimental stage, shows following drawbacks: